The present invention relates to a control system for transmission devices equipped with a high-efficiency coding scheme in a communication network, including a telephone networkxe2x80xa2ISDN (Integrated Services Digital Network).
With the recent progress in high efficiency speech coding technologies, it is now possible to transfer a high-quality speech signal at low speeds; however, such a high-efficiency coding scheme has a defect of degradation of speech quality by repeated decoding/coding of the speech signal. As a solution to this problem, there has been proposed such a system as depicted in FIG. 15, which comprises exchanges 101a, 101b, 101c and 101d, transmission devices 102b, 102d and 102f equipped with a high-efficiency coding scheme and directly connected to input or incoming lines (channels from a calling party) of the exchanges, respectively, and transmission devices 102a, 102c and 102e similarly equipped with a high-efficiency coding scheme and directly connected to output or outgoing lines (channels to a called party) of the exchanges, respectively. In this system, specific information is transferred (as indicated by 10d, 10e, 10f, 10g, 10h and 10i) over speech paths between some of the exchanges and the transmission devices preceding or following them and between transmission devices preceding and following the other exchanges. The transmission devices 102b, 102c, 102d and 102e, which have received the specific information, do not decode/encode a speech signal encoded with high efficiency but only perform switching of the coding rate for matching it to the speed of circuit switching. On the other hand, the transmission devices 102a and 102f, which have not received the specific information, decode/encode the speech signals encoded with high efficiency. This avoids the necessity for decoding/coding in exchanges which involve relay processing, thereby suppressing degradation of speech quality.
However, when transmission devices of the same characteristic cannot be used over the entire communication channel as depicted in FIG. 16, decoding/coding is unavoidable in transmission devices 112a, 112b, 112c and 112d connected to exchanges 111a, 111b, 111c and 111d which involve relay processing; hence, speech quality is inevitably degraded.
Further, since this is not a communication system of the type that exchanges pass therebetween information concerning channel conditions, it is impossible to choose, if any, a transmission line over which communication could be done without degradation. Moreover, as shown in FIG. 17, since in some exchange (121c, for instance) no speech channel has been set up from a calling party to a called party until the latter answers the call, a transmission device 122d connected to the incoming path of the exchange 121c receives specific information which is transferred over the channel, and only performs converting of the coding rate of high-efficiency-coded speech signal for matching it with the speed of circuit switching in that exchange without decoding/coding of the speech signal. On the other hand, a transmission device 122e connected to the outgoing path of the exchange 121c decodes/encodes the high-efficiency-coded speech signal encoded without receiving specific information (12h) which is transferred over the channel. Hence, the coding/decoding at either side of the exchange 121c does not match with the coding/decoding at the other side thereof and this exchange cannot relay the speech signal, giving rise to a problem that it cannot transfer the speech signal or acoustic signal before the called party answers.
It is an object of the present invention to provide a control system for transmission devices equipped with a high-efficiency coding scheme in a communication network which avoids degradation of the quality of an acoustic signal being transferred and permits its efficient transfer.
To attain the above object, the control system for transmission devices equipped with a high-efficiency coding function in a communication network according to the present invention has a structure in which information on a high-efficiency coding scheme used in the preceding transmission device is sent from the preceding exchange to the current and following exchanges through the use of an out-band signaling system, and based on this information, it is determined whether to prevent the transmission devices connected to the current and following exchanges from decoding/coding of the transferred acoustic signal by the high-efficiency coding function for the transfer of the signal or avoid the use of these transmission devices.
That is, according to the present invention, there is provided a control system for transmission devices each equipped with a high-efficiency coding scheme in a communication network in which a first transmission line through each of the transmission devices provided with a coding/decoding circuit for high-efficiency coding/decoding scheme of an acoustic signal and a second transmission line not through said each transmission device are connected to one of a predetermined number of exchanges, characterized in: that, in case of starting a transfer of a high-efficiency-coded acoustic signal from one of the predetermined number of exchanges, the type of high-efficiency coding scheme to be used and an identifier, which indicates that the acoustic signal has been coded or decoded by said high-efficiency coding scheme, are sent as processing information on the coded acoustic signal which is transferred from the transfer-starting exchange to the following exchange in the communication network, the processing information being contained in a call control signal indicative of the start of a call; and that each of the exchanges in the communication network, through which the coded acoustic signal passes in its transfer, uses the processing information transferred thereto to select the first transmission line or the second transmission line as an outgoing line so as to avoid degradation of the quality of the acoustic signal due to its multi-stage coding and decoding for the high-efficiency coding scheme and to efficiently transfer the acoustic signal.
The transfer starting exchange is provided with a call controller for effecting a call control operation by a processing function of an out-band signaling system and a switching part for circuit switching, the call controller of the exchange being connected to the transmission device via a transmission switching signal link.
The transmission device is provided with a coding/decoding controller, which, based on the processing information, controls whether to enable the high-efficiency coding/decoding of the acoustic signal or disable the high-efficiency coding/decoding in the transmission device, and a coding rate converter for converting the coding rate of the coded acoustic signal, the coding/decoding controller of the transmission device being connected to a call controller of the exchange via a transmission switching signal link.
The processing information is analyzed in the call controller of the exchange, and when the transfer of an acoustic signal coded with the same high-efficiency coding scheme as the said high-efficiency coding scheme of said first transmission line preceding said exchange is possible over the first transmission line immediately following the exchange, the exchange selects as an outgoing line the first transmission line through the transmission device and provides an instruction via the transmission switching signal link to the coding/decoding controller of each of the transmission devices preceding and following the exchange connected thereto so that the exchange permits the passage therethrough of the coded acoustic signal intact without coding or decoding the same, and provides onto the immediately following first transmission line a signal obtained by converting the coding rate of the coded acoustic signal in the coding rate converter.
The processing information is analyzed in the call controller of the exchange, and when the transfer of an acoustic signal coded with the same high-efficiency coding scheme as the said high-efficiency coding scheme of said first transmission line preceding said exchange is impossible over the first transmission line immediately following the exchange, the exchange selects as an outgoing line the second transmission line not through the transmission device and provides an instruction via the transmission switching signal link to the coding/decoding controller of the transmission device preceding the exchange so that the transmission device decodes the coded acoustic signal, and provides onto the immediately following second transmission line the signal decoded to an acoustic signal of non high-efficiency coding scheme.
The processing information is analyzed in the call controller of the exchange, and when it is judged that the transfer of an acoustic signal coded with a second high-efficiency coding scheme different from the said high-efficiency coding scheme is possible over the first transmission line immediately following the exchange, and that degradation of the quality of the coded acoustic signal will be avoided in the course of its coding by the second high-efficiency coding scheme, the exchange: selects as an outgoing line the first transmission line through the transmission device: provides an instruction via the transmission switching signal link to the coding/decoding controller of the transmission device preceding the exchange so that the transmission device decodes the coded acoustic signal: provides an instruction via the transmission switching signal link to the decoding/coding controller of the transmission device following the exchange so that the transmission device encodes the acoustic signal by the second high-efficiency coding scheme; and transfers to the immediately following first transmission line a signal obtained by the second high-efficiency coding scheme.